Cochlear implants (CI) help profoundly deaf or severely hearing impaired persons to perceive environmental sounds. Unlike conventional hearing aids, which just apply an amplified and modified sound signal, a cochlear implant is based on direct electrical stimulation of the auditory nerve. The intention of a cochlear implant is to stimulate nervous structures in the inner ear electrically in such a way that hearing impressions most similar to normal hearing are obtained.
A cochlear implant system essentially consists of two parts, an external speech processor and the implanted stimulator. The speech processor contains a power supply and is used to perform signal processing of the acoustic signal to extract stimulation parameters for the implanted stimulator. The implanted stimulator generates stimulation patterns and conducts them to auditory nervous tissue by an electrode array which usually is positioned in the scala tympani in the inner ear. Inductive coupling across the skin is used to transfer both the required electrical power and the processed audio information to the implanted components. An external transmitter coil (coupled to the external signal processor) is placed on the skin adjacent to a subcutaneous receiver coil (connected to an implanted receiver). Often, a magnet in the external coil structure interacts with a corresponding magnet in the subcutaneous secondary coil structure. This arrangement inductively couples a radio frequency (rf) electrical signal to the receiver, which is able to extract from the rf signal both the audio information for the implanted portion of the system and a power component to power the implanted system.
Some recipients of cochlear implants (CI's) also have problems with their vestibular system, which increases the risk that they will loose their balance and fall. When that happens, the side of their head containing the implant may receive a mechanical impact, which among other things, may result in damage to the implant.
Thus, the implant needs to be designed to withstand mechanical impacts. But making an implant very robust may have the disadvantage that it becomes too physically large (especially with children). Furthermore, if the implant is extremely strong, there is additional risk that a fall related mechanical impact may cause a bone fracture of the implant bed. One alternative possibility is to place the implant anatomically at a location which is less prone to a mechanical impact. But that solution is not possible for every implant and stimulator type, for example, because the implanted electrode wires might be too long, etc.